Dispersion strengthened copper (DSC) has high strength and electrical conductivity at room temperature. It also has excellent structural stability up to temperatures approaching the melting point of the matrix (1083.degree. C.; 1981.degree. F.). This stability is responsible for its excellent strength retention characteristics at and after exposure to elevated temperatures. These properties are derived from the relatively small amounts (e.g., 0.05% to 5.0% as the metal) of dispersoid which is generally a stable metal oxide, especially a refractory metal oxide, such as alumina, silica, magnesia, thoria, beryllia, zirconia or the like. Alumina, Al.sub.2 O.sub.3, generated internally from aluminum metal by internal oxidation is commonly used. Reference may be had to U.S. Pat. No. 3,779,714 for one internal oxidation method and various dispersion strengthened copper compositions producible thereby. The disclosure of that patent is incorporated herein by reference. Reference may also be had to U.S. Pat. Nos. 4,274,873, 4,315,770 and 4,315,777 for other methods of producing dispersion strengthened copper powder. These patents are also incorporated herein by reference.
There are many applications in the field where one or more of the basic characteristics of dispersion strengthened copper are important, but one or more additional requirements render dispersion strengthened copper unsuitable. A case in point is eyeglass frame wire. This application, for example, requires that the material have strength retention ability when exposed to brazing temperatures, generally in the 1200.degree. F. to 1600.degree. F. (649.degree. C. to 871.degree. C.) range. In addition, it must have spring properties superior to what dispersion strengthened copper has.
The spring properties of dispersion strengthened copper can be significantly improved by alloying the copper with other metals (in addition to the solute metal for internal oxidation), particularly tin. Copper alloy metallurgy teaches that copper-tin alloys (bronzes) do indeed have superior spring properties. A dispersion strengthened copper-tin bronze has the desired combination of elevated temperature strength retention and high elastic limit. The presence of aluminum and aluminum oxide (for dispersion strengthening) surprisingly does not detract from the ability of the tin to impart elasticity to the final product. Other dispersion strengthened copper/metal alloys are also useful, e.g., DSC/silicon; DSC/aluminum/silicon; DSC/nickel/tin; DSC/zinc/tin; DSC/tin/phosphorus; DSC/nickel/phosphorus.
The closest prior art of which we are aware is the U.S. patent to Gregory No. 3,026,200 directed to a method of introducing a hard phase into a metallic matrix which matrix can be an alloy of several metals including alloys of copper, useful herein. The procedure used to arrive at a dispersion strengthened copper alloy is quite different, however. According to Gregory, the finely divided copper alloy powder is internally oxidized from a surface oxide of the maxtrix followed by consolidating.
It has been found that where a prealloy is made followed by internal oxidation from decomposition of an external oxide as in Gregory, the rate of internal oxidation, which is O.sub.2 -diffusion rate limited, is one tenth to one twentieth of that achieved with internal oxidation of aluminum, for example, in a copper/aluminum alloy using Cu.sub.2 O as an oxidant. The presence of alloying elements inhibits oxygen diffusion from the surface and makes the prior art process commercially unattractive.